1. Field of the Invention
The present invention relates generally to a gear device. More particularly, the present invention relates to a low noise type gear device wherein leakage of sound, generated by gear meshing and collision of splash and drops of a lubricant with a wall surface of the casing, and sound attributable to resonance of the casing, can be reliably prevented.
2. Description of the Related Art
Various conventional gear devices of the aforementioned type are in practical use. Among them, a typical conventional gear device (reduction gear) will briefly be described below with reference to FIG. 3.
In FIG. 3, reference numeral 1 designates a casing which is of an entirely closed box-shaped configuration. The casing 1 includes a side wall 1A and a side wall 1B. First bearing set 2A, second bearing set 2B and third bearing set 2C are fitted into both the side walls 1A and 1B of the casing 1. An input shaft 4 is rotatably supported by the third bearing set 2C while a first gear 3A is fixedly mounted on the input shaft 4. An intermediate shaft 5 is rotatably supported by the second bearing set 2B while a second gear 3B and a fourth gear 3D are fixedly mounted on the intermediate shaft 5. Similarly, an output shaft 6 is rotatably supported by the first bearing set 2A while a third gear 3C is fixedly mounted on the output shaft 6.
The fourth gear 3D is fixedly mounted adjacent to the second gear 3B on the intermediate shaft 5. Accordingly, the first gear 3A meshes with the second gear 3B and the third gear 3C meshes with the fourth gear 3D.
One end 4a of the input shaft 4 projects outward of an outer wall 1a of the casing 1, while one end 6a of the output shaft 6 projects outward of the outer wall 1a of the casing 1.
A sound-proofing member 7, molded of a rubber, a synthetic resin or the like, covers the whole outer wall 1a of the casing 1 so as to prevent sound generated by meshing engagement of the gears 3A to 3D and sound generated by collision of splash and drops of a lubricant utilized in the device with an inner wall 1b of the case 1 from traveling to the outside of the casing.
Although not illustrated for the purpose of simplification, another conventional gear device of the aforementioned type is constructed such that the bearing sets are arranged on the inner wall 1b of the casing 1, as opposed to being fitted into the wall. Otherwise, operation of this device is similar to that of the device illustrated in FIG. 3.
Conventional gear devices, constructed in the above-described manner, have several limitations. Specifically, in the case of the first-mentioned conventional gear device, a large space is required for installation, and moreover, it requires a large quantity of sound-proofing materials. Consequently, it is expensive to manufacture and apply.
Also, heat generated by meshing engagement of the respective gears in the casing cannot be easily diverged to the outside of the sound-proofing cover through the casing. For this reason, the bearings and other associated components may become thermally damaged.
In addition, the aesthetic appearance of the gear device is degraded and maintenance is difficult to perform due to the sound-proofing material on the casing.
In the case of the second conventional gear device discussed above, it unavoidably requires even larger dimensions, resulting in an increase in production cost. It should be added that this type gear device also does not operate satisfactorily.